1. Field of the Invention
The present invention relates to an improvement in a direct drive motor system including a synchronous resolver of a variable reluctance type and a cable to connect the resolver and a driver unit.
Hereinafter, in a case of that “synchronous resolver” is called simply “resolver”, the “resolver” is used as same meaning as the “synchronous resolver”.
In particular, the present invention relates to an improvement in a technique for correcting variations in windings of a synchronous resolver to thereby secure compatibility between products.
In particular, the present invention relates to a wiring structure for a cable for transmitting a resolver signal which is used to detect the rotation angle position of a motor.
2. Description of the Related Art
As a detector for detecting the rotation angle position of a direct drive motor which drives a load directly without using a decelerator, in Japanese Patent No. 3060525, there is disclosed a resolver apparatus which detects a rotation angle position showing the absolute position relationship of a rotor and a stator from a homopolar resolver signal obtained from a homopolar resolver structured such that the fundamental wave components of a reluctance in the airgap between rotor iron core of the homopolar resolver and a stator iron core of the homopolar resolver provides one cycle when the rotor iron core rotates once, and detects a high-resolution rotation angle position from a multipolar resolver signal obtained from a multipolar resolver structured such that the fundamental wave component of the reluctance provides a plurality of cycles when the rotor iron core rotates once, thereby being able to provide a resolver apparatus which can provide a high resolution and can detect the absolute position.
For example, in the case of a resolver having three phases, output signals (see FIG. 19) from the respective phases (A phase, B phase, and C phase) of the resolver can be expressed in the following manner, with the higher-order components thereof neglected (FIG. 20 shows a case of the A phase):φ A=(A1+A2 sin θ)×sin ωtφ B=(B1+B2 sin (θ−2/3π))×sin ωtφ C=(C1+C2 sin (θ−4/3π))×sin ωtwhere ω expresses an angular velocity corresponding to the frequency f of the exciting signal of the resolver (that is, ω=2 π f).
These signals are converted into two-phase signals using, for example, a phase converter circuit and further they are converted into digital position (angular position) signals using, for example, a known resolver digital converter (RDC). By the way, as the RDC, there can be used a converter having a correction function (for example, a built-in ROM) for correcting higher-order component errors peculiar to the types of resolvers. There can be a drive unit which contains an A/D converter for converting the output signals of the respective phases into digital signals and executing the following processings using software.
As disclosed in JP-B-7-44813, as a detector for detecting the angle position of a servomotor system, there is used a resolver. In the resolver, a rotor iron core shifts in angle with respect to a stator iron core and a reluctance component in a gap existing between the rotor and stator iron cores is thereby caused to vary; that is, using such variation in the reluctance component, the resolver detects the rotation angle position of the servomotor system. On a resolver stator of three phases type, there are wound detect signal lines of A, B and C phases respectively having an electrical angle phase difference of 120°. In case where the windings of the respective phases vary in the winding number, inductance, and resistance values, there is generated an imbalance in the signals of the three phases to cause an error in a true value, thereby degrading the precision of a position detector.
On the other hand, in the conventional resolver apparatus, in a three-phase AC exciting winding is directly wound around a substantially T-shaped magnetic pole projectingly provided on a stator, it is also very difficult to realize a uniform winding state for a large number of magnetic poles, which causes the resolver signals between the respective phases to vary. Since such variations according to individual motors are caused by variations in the sizes of the d.c. components (A1, B1, C1) of the respective phases, the above-mentioned correction by the driver is not able to cope with such variations. Therefore, conventionally, a polyphase signal from a resolver disposed on a direct drive motor having correction data in order to correct above variations is converted to a 2-phase output signal (sin signal, cos signal) by a phase converter circuit disposed in a drive unit; and, after then, there are taken in the correction data for correcting imbalance between the respective phases caused by the variations in the resolver signals, and there is obtained a digital position signal by a resolver digital converter (JP-A-2000-262081).
On the other hand, in a conventional direct drive motor system, a resolver signal cable (a resolver cable) for supplying, an exciting signal to a resolver and, at the same time, for obtaining a resolver signal from the resolver is used to connect together a drive unit and a direct drive motor. In selection of a resolver signal cable used to transmit an analog signal, preferably, there may be selected a resolver signal cable which not only has a thick line diameter but also, in order to restrict electrical interference between signal lines, has a small line electrostatic capacity within the cable.
However, the correction data to be loaded into a drive unit vary according to individual direct drive motors. Accordingly, when the direct drive motor or drive unit is replaced as a simple element due to trouble or for maintenance, since they are not compatible with others, the direct drive motor system comprising the direct drive motor, drive unit and cables (resolver cables, motor cables) for connecting these motor and unit must be replaced as a whole.
As measures to deal with this, in JP-A-2000-262081, there is disclosed a resolver apparatus structured such that a motor main body stores correction data therein and a memory disposed on the driver side is used to read the correction data. In this resolver apparatus, however, the correction data must be added to the motor side in the form of e.g. a ROM and also there is necessary an operation in which the correction data are read by the memory on the driver side.
Also, conventionally, as a resolver cable for transmitting a resolver signal to the drive unit, a required number of resolver signal lines for detection of signals are disposed at arbitrary positions within the cable. However, in case where the position relationship of the respective detect signals within the resolver cables is asymmetric, due to variations in the lengths of the cables, there is caused electrical interference. And, in the case of the resolver cables used in the direct drive motor system, there also arises a problem as to their compatibility.
Therefore, in the case of the conventional resolver signal cable, as shown in FIGS. 16 to 18, the connection thereof is made without taking into account the arrangement between the exciting signal line and the respective phase detect signal lines and the arrangement between the respective phase detect signal lines; and, due to such connection, there is caused an imbalance in the values of the electrostatic capacity between the exciting signal line and the respective phase detect signal lines as well as in the values of the electrostatic capacity between the respective phase detect signal lines. FIG. 16 is a section view of a resolver signal cable of a one-phase excitation three-phase output- type, in which reference character 150 designates a resolver signal cable, 151 an A-phase detect signal line, 152 a B-phase detect signal line, 153 a C-phase detect signal line, and 154 an exciting signal line (a common signal line) which is used to supply an exciting signal from a driver unit to a resolver apparatus. In the resolver signal cable of this type, where the values of the electrostatic capacity between the exciting signal line 154 and the A-phase detect signal line 151, B-phase detect signal line 152, C-phase detect signal line 153 are respectively expressed as CA, CB, CC, there is obtained CA=CC≠CB, namely, there is found an imbalance between them. Further, assuming that the value of the electrostatic capacity between the A-phase detect signal line 151 and B-phase detect signal line 152 is expressed as CAB, the value of the electrostatic capacity between the B-phase detect signal line 152 and C-phase detect signal line 153 is expressed as CBC, and the value of the electrostatic capacity between the C-phase detect signal line 153 and A-phase detect signal line 151 is expressed as CCA, then there is obtained CAB=CBC≠CCA, that is, there is found an imbalance between them. This imbalance, when the length of the cable is changed, has an influence on the respective phase detect signal lines and thus gives rise to an error in the absolute precision of the resolver signal cable.
Now, FIG. 17 is a section view of a resolver signal cable which can provide two kinds of three-phase outputs from one-phase excitation, in which 160 stands for a resolver signal cable, 161-163 respectively designate a first A phase detect signal line, a first B phase detect signal line and a first C phase detect signal line, and 164-166 respectively stand for a second A phase detect signal line, a second B phase signal line and a second C phase detect signal line. 167 stands for an exciting signal line (a common signal line). In the resolver signal cable of this type, where the values of the electrostatic capacity between the exciting signal line 167 and the first A phase, B phase and C phase detect signal lines 161-163 are respectively expressed as C1A, C1B and C1C, and the values of the electrostatic capacity between the exciting signal line 167 and the second A phase, B phase and C phase detect signal lines 164-166 are respectively expressed as C2A, C2B and C2C, there are obtained C1A≠C1B≠C1C and C2A≠C2B≠C2C, that is, there is found an imbalance between them. Also, in the case of the respective phase detect signal lines as well, where the values of the electrostatic capacity between the first A and B phases, between the first B and C phases, and the first C and A phases are respectively expressed as C1AB, C1BC and C1CA, and the values of the electrostatic capacity between the second A and B phases, between the second B and C phases, and the second C and A phases are respectively expressed as C2AB, C2BC and C2CA, there are obtained C1AB=C1BC≠C1CA and C2AB=C2BC≠C2CA, that is, there is found an imbalance between them.
Now, FIG. 18 is a section view of another structure of a resolver signal cable which provides two kinds of three-phase outputs for one phase excitation, in which 170 designates a resolver signal cable, 171-173 respectively stand for first A phase, B phase and C phase detect signal lines, and 174-176 respectively represent second A phase, B phase and C phase detect signal lines. 177 stands for an exciting signal line (a common signal line). In the resolver signal cable of this type, where the values of the electrostatic capacity between the exciting signal line 177 and the first A phase, B phase and C phase detect signal lines 171-173 are respectively expressed as C1A, C1B and C1C, and the values of the electrostatic capacity between the exciting signal line 177 and the second A phase, B phase and C phase detect signal lines 174-176 are respectively expressed as C2A, C2B and C2C, there are obtained C1A=C1B=C1C and C2A=C2B=C2C, that is, it is found that they balance well. However, where the values of the electrostatic capacity between the first A and B phases, between the first B and C phases, and the first C and A phases are respectively expressed as C1AB, C1BC and C1CA, and the values of the electrostatic capacity between the second A and B phases, between the second B and C phases, and the second C and A phases are respectively expressed as C2AB, C2BC and C2CA, there are obtained C1AB=C1BC≠C1CA and C2AB=C2BC≠C2CA, that is, there is found an imbalance between them.
As described above, in case where the values of the electrostatic capacity between the exciting signal line and the respective phase detect signal lines of the resolver signal cable do not balance well, when the length of a cable is changed freely, or when a very long cable is used, there occurs electrical interference between the signal lines due to the imbalance between the values of the electrostatic capacity thereof, which gives rise to errors in the measurement of the resolver. That is, the conventional manner of cable selection, in which a cable is selected simply because it is small in line electrostatic capacity, is not always be able to secure the satisfactory fulfillment of the function of the resolver. Especially, since a signal flowing in a resolver signal cable is a minute analog current, there is influenced by the length of the cable, which is prone to degrade the precision of the resolver.